1. Field of the Invention
The invention relates to a light emitting diode (LED) driving apparatus. Particularly, the invention relates to a method for holding a driving voltage of a LED driving apparatus.
2. Description of Related Art
FIG. 1 is a schematic diagram of a conventional light emitting diode (LED) driving apparatus 100. In the LED driving apparatus 100, in order to drive a LED string 130 to produce a normal brightness, a power converter 120 of the LED driving apparatus 100 receives and transmits a cross voltage of the conducted LED string 130 through a current driver 122 to serve as a reference voltage VFB, and the LED driving apparatus 100 adjusts a magnitude of a driving voltage Vout according to the reference voltage VFB.
On the other hand, the LED driving apparatus 100 further receives a dimming status signal DIM for dimming the LED string 130. Namely, when the dimming status signal DIM instructs the LED 130 to stop emitting light, a pulse width modulation (PWM) signal PWM generated by a power conversion controller 121 turns off a power transistor switch T1 to stop power conversion. Meanwhile, the driving voltage Vout decreases along with time. When the dimming status signal DIM instructs the LED 130 to start emitting light, the power conversion controller 121 generates the effective PWM signal PWM according to the reference voltage VFB and a feedback voltage OVS to switch the power transistor switch T1 to reactivate the power conversion operation, so that the driving voltage Vout is increased.
During the operation of the LED driving apparatus 100, if a time duration that the dimming status signal DIM instructs the LED string 130 to stop emitting light is excessively long, the driving voltage Vout is greatly decreased, and when the LED string 130 is restarted to emit light, in order to quickly increase the driving voltage Vout, an inductor L1 of the power converter 120 may generate a large inducting current IL. Such derived large inducting current IL may cause a severe electro-magnetic interference (EMI), and may also cause damage of components in the LED driving apparatus 100.